Most strung hand held sporting rackets have a striking surface or face formed of two intersecting sets of parallel strings suspended by and enclosed by an oval frame. One set extends generally parallel to the handle of the racket and may be called the longitudinal strings, while the other set extends generally transversely of the handle and may be called the transverse strings. In such rackets, vibrations are produced in the racket face when a projectile is struck. These vibrations are most noticeable in rackets used in playing games involving a ball, particularly tennis. The vibrations are most severe when the ball does not strike the racket face in the center thereof, but strikes it at a distance spaced from the center or when the hit is not considered to be a "solid" hit. Initially, rather large vibration is detected in the racket face and this initial vibration is followed by a series of smaller vibrations which eventually die out with time. Such vibrations are transmitted generally along the transverse and longitudinal strings of the racket, to the frame surrounding and holding the strings, and eventually down the racket handle to the hand and then the arm of the player. The more one plays, the greater is the exposure to such vibrations. It has been shown that a player who has been subject to extensive periods of racket-induced vibrations can sustain injury to his or her arm. Thus, it is considered desirable to reduce such vibrations both for the comfort of the player and for the protection of the player.
In recent years, the use of composite racket constructions and other advanced technologies has allowed the tension of the racket strings to be increased to levels of 75 pounds or more. These higher tensions produce greater and more sustained vibration levels in the racket face and also a greater transfer of vibrations to the handle.
In the past, most efforts at reducing these vibrations have been directed towards the racket construction. Such efforts have included changing the structural material of the racket, and in recent years, fibrous materials such as carbon fibers and boron fibers have been added to the racket head and handle structure. Some previous efforts at reducing vibrations by modifying the racket structure are shown in U.S. Pat. Nos. 3,941,380 and 2,732,209. However, even with these improved racket constructions, vibrations still persist. In addition, different types of racket strings are known to inhibit vibrations better than others. In particular, strings made of natural catgut have a lower tendency to produce vibrations than plastic strings. However, other considerations enter into the choice of materials for the racket and for the strings, and often players prefer materials for higher performance which do not necessarily produce a lower level of vibration.
Another device for dampening the vibrations in the racket strings is shown in U.S. Pat. No. 4,180,265. In this device, two strings are coupled together by a device which interlocks them. However, the device shown in this patent has not been entirely successful in reducing vibrations in rackets, particularly in tennis rackets. In addition, the device shown in U.S. Pat. No. 4,180,265 is sometimes difficult to attach to the racket face, and can interfere with the flight of the ball if struck by the ball.
Other devices which interconnect the strings of a racket face for other purposes include U.S. Pat. Nos.: 4,368,886; 3,921,979; 4,078,796; 4,168,065; and 1,682,199.